how to check if my BMW 3 Series F30/F31 (2012-2019) alternator is bad

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench.
• Disconnect the negative battery terminal to ensure safety.

2. Remove the Alternator

• Sub-steps:
  1. Remove the drive belt by loosening the tensioner pulley.
  2. Disconnect the electrical connectors from the alternator.
  3. Unbolt the alternator from its mounting bracket using a socket set.
  4. Carefully lift the alternator out of the engine bay.

3. Inspect and Test the Alternator

• Sub-steps:
  1. Visually inspect the alternator for any physical damage or wear.
  2. Use a multimeter to test the output voltage of the alternator by connecting it to the alternator's output terminal.
  3. Check the diodes by performing a diode test with the multimeter; a shorted diode will show continuity in both directions.

4. Replace the Alternator (if necessary)

• Sub-steps:
  1. If the alternator is faulty, install the new alternator into the mounting bracket.
  2. Reconnect the electrical connectors securely.
  3. Reinstall the drive belt and ensure proper tension.
  4. Reconnect the negative battery terminal.

5. Final Checks

• Sub-steps:
  1. Start the engine and verify that the battery warning light is off.
  2. Measure the output voltage again to confirm it is within the specified range.